This invention relates to a back-light system used in a liquid crystal television, a liquid crystal display, a general indication system, etc. and in particular to an inexpensive back-light system having a small unevenness, preventing locally high brightness intensity in the form of the back-light, and suitable for making the brightness uniform over a luminous surface.
A prior art device for making the brightness of a luminous surface uniform was such that black or silver dots or a plane film having a reflective layer whose transmission amount of light was approximately inversely proportional to the amount of light emitted from the luminous surface are provided on the back-light surface or the luminous plane surface, as disclosed in Japanese Utility Model Application Laid-Open No. 6134188 and JP-A-55-15126.
The prior art technique is disadvantageous from the point of view of reduction of the cost because the printed film or the direct printing on the lamp is costly and also from the point of view of the efficiency because the transmission of the light coming from the back-light source is lowered over the whole surface due to a film provided over the whole surface between the luminous surface and the back-light source. Further, both examples were lacking in mass-productivity and easiness of assembly, because the printing for preventing unevenness of brightness and the positioning of the film are difficult.